Annual and between-colony variation in productivity of Arctic Terns in West Iceland

Figures & data

Figure 1. Location and approximate size (number of pairs) of Arctic Tern study colonies on Snaefellsnes peninsula and the location of the peninsula in western Iceland (inset). Sty, Stykkisholmur; Ber, Berserkseyri; Ska, Skallabudir; Tho, Thordisarstadir; Gru, Grundafjordur; Lar, Larvadall; Rif, Rif; Arn, Arnarstapi; Hra, Hraunsmuli; Lan, Langaholt; Sta, Stakkhamarsnes.

Table 1. Numbers of Arctic Tern nests monitored in each colony in each year of the study.

Colony	2008	2009	2010	2011
Hra	–	14	9	–
Ber	–	18	11	17
Sty	12	21	28	14
Sta	11	–	–	–
Gru	–	23	25	19
Tho	–	20	–	–
Lar	–	24	16	–
Ska	–	34	–	–
Lan	–	33	48	15
Arn	25	34	28	–
Rif	18	51	36	31
Total	66	272	201	96
Note. Colony order is presented according to colony size (from smallest (top) to largest (bottom)). See Fig. 1 for colony locations and details.

Table 2. Annual variation in components of productivity of Arctic Tern nests on colonies across the Snaefellsnes peninsula, West Iceland.

		Clutch size	Hatched per egg laid	Fledged per egg laid	Fledged per chick hatched	Fledged per pair
2008	Mean	2.03	0.93	0.02	0.02	0.05
	sd	0.39	–	–	–	–
	n	66	134	134	124	66
2009	Mean	1.74	0.93	0.06	0.07	0.11
	sd	0.53	0.24	0.22	0.24	0.35
	n	272	474	474	427	272
2010	Mean	1.82	0.89	0.28	0.34	0.51
	sd	0.44	0.25	0.36	0.40	0.51
	n	201	366	366	297	201
2011	Mean	1.40	0.83	0.09	0.13	0.11
	sd	0.57	0.35	0.28	0.33	0.35
	n	96	134	134	85	96
Note. See Table 1 for details of sample sizes.

Table 3. Results of generalized linear models of annual and between-colony variation in five components of productivity of Arctic Terns on Snaefellsnes peninsula, West Iceland, between 2009 and 2011.

		Colony	Year
Clutch size	W	4.9	5.8
	df	9	2
	P	0.84	0.06
Hatching success	W	4.2	1.2
	df	9	2
	P	0.90	0.54
Fledged per egg laid	W	25.2	35.9
	df	6	2
	P	<0.001	<0.001
Fledged per egg hatched	W	21.4	33.5
	df	6	2
	P	<0.01	<0.001
Fledged per pair	W	30.1	46.8
	df	6	2
	P	<0.001	<0.001
Note. See Table 1 for details on sample sizes. The colony*year interaction was not significant in any model (W 4 < 4.14, P > 0.39 in all cases) and was removed.

Figure 2. Annual and between-colony variation in mean (±se) Arctic Tern (a) clutch size, (b) hatching success, (c) fledged chicks per eggs laid, (d) fledged chicks per chick hatched and (e) fledged chicks per nest. Colony order is presented according to colony size (from smallest (left) to largest (right)). Black dashed lines indicate zero values. See Fig. 1 for colony locations and details.